The present invention relates generally to medical devices and methods. More specifically, the present invention relates to apparatus and methods for deploying a variable length luminal medical prosthesis comprised of multiple linked or coupled prosthetic stent segments.
Stenting is an important treatment option for patients with coronary artery disease and has become a common medical procedure. The procedure is mainly directed at revascularization of stenotic vessels where a blocked artery is dilated and a stent is placed in the vessel to help maintain luminal patency. The stent is a small, tubular shaped device that can be expanded in a diseased vessel, thereby providing support to the vessel wall which in turn helps to maintain luminal patency.
Restenosis, where treated vessels such as coronary arteries tend to become re-occluded following stent implantation, was a problem in early stent technology. However, recent improvements in stent design, delivery systems and techniques along with the development of drug eluting stents have significantly reduced restenosis rates. Because of the improved efficacy of stenting, the number of stenting procedures has dramatically increased worldwide.
A balloon expandable stent, also referred to as a luminal prosthesis, is delivered to the coronary arteries using a long, flexible vascular catheter with a balloon on the distal end over which the stent is mounted. The delivery catheter is introduced into the vascular system percutaneously through a femoral, brachial, radial artery or other access point. Once the stent is delivered to the target treatment site, the delivery catheter balloon is expanded which correspondingly expands and permanently deforms the stent to a desired diameter. The balloon is then deflated and removed from the vessel, leaving the stent implanted in the vessel at the lesion site.
Self-expanding stents are another variation of luminal prosthesis where the stent is constrained during delivery and then released at a desired location. When the stent is released from the constraining mechanism, the stent resiliently expands into engagement with the vessel wall. The delivery catheter is then removed and the stent remains in its deployed position.
With current stents lesion size must be assessed in order to determine the appropriate stent length required to effectively cover the lesion. Fluoroscopy and angiography are therefore used to evaluate the lesion prior to stent delivery. A stent of appropriate size is then delivered to the lesion. Sometimes, however, lesion length cannot be assessed accurately and can result in the selection of stents which are not long enough to adequately cover the target lesion. To address this shortfall, an additional stent must be delivered adjacent to the initially placed stent. When lesion length requires multiple stents to be delivered, multiple delivery catheters are required since typically only one stent is provided with each delivery catheter. The use of multiple delivery catheters results in greater cost and longer procedure time. To overcome this shortcoming, recent stent delivery systems have been designed to streamline this process by allowing multiple stent segments to be delivered simultaneously from a single delivery catheter, thereby permitting customization of stent length in situ to match the size of lesion being treated.
Various designs have been proposed for custom length prostheses such as those described in U.S. patent application Ser. No. 10/306,813 filed Nov. 27, 2002 which is incorporated herein by reference. These designs utilize delivery systems pre-loaded with multiple stent segments, of which some or all of the stent segments can be delivered to the site of a lesion. This allows the length of the prosthesis to be customized to match the lesion size more accurately.
While the capability of customizing stent length in situ provides significant benefits over fixed length devices, it has been found that such segmented stent systems may have drawbacks under certain circumstances. For example, when vessels are highly tapered or have other irregularities in diameter, a single balloon of constant diameter may be unable to expand all of the stent segments to engage tightly with the vessel wall. In this situation, some of the segments in a multi-segment prosthesis might be under-deployed resulting in incomplete apposition with the vessel wall along the entire lesion length. This may then require a second high-pressure dilatation of the underdeployed prostheses to ensure full apposition to the vessel wall. If the segments are not fully apposed, there is a risk that they could tilt or move within the vessel.
For these and other reasons, stent delivery systems and methods are needed which can accommodate tapered vessels and minimize or prevent a stent segment from moving, dislodging or tilting in the vessel following deployment. Such stent systems should also permit stent length customization in situ and allow treatment of multiple lesions of various sizes, without requiring removal of the delivery catheter from the patient. At least some of these objectives will be met by the present invention.